1. Field
Various embodiments of the present invention relate to a resistive memory device, and more particularly, to a read operation of a resistive memory device.
2. Description of the Related Art
Generally, since data programmed in a laser fuse may be determined by whether or not the laser fuse is cut by a laser, a laser fuse is programmable only in a wafer state. However a laser fuse is not programmable after the wafer is packaged.
An electrical fuse, hereinafter, referred to as an e-fuse, is used to overcome such limitations of the laser fuse. The e-fuse uses a transistor that stores data based on the change in the resistance between a gate and a drain/source of the transistor.
FIG. 1 is a diagram illustrating an e-fuse formed of a transistor operating as a resistor or a capacitor.
Referring to FIG. 1, the e-fuse includes a transistor T having a gate G and a drain/source D/S to which a ground voltage is supplied.
When a power source voltage, which is tolerable to the transistor T, is applied to the gate G, the e-fuse operates as a capacitor C. Thus, there is no current flowing between the gate G and the drain/source D/S. However, when a high voltage that is intolerable to the transistor T is applied to the gate G, a gate oxide of the transistor T is broken that shorts the gate G and the drain/source D/S from each other, thus the e-fuse operates as a resistor R. Accordingly, a current flows between the gate G and the drain/source D/S of the e-fuse. The data of the e-fuse is recognized by the resistance value between the gate G and the drain/source D/S.
FIG. 2 is a diagram illustrating a memory device including an e-fuse, that is, a resistive memory element.
Referring to FIG. 2, the memory device includes a resistive memory element M, a data line DL, a load 210 and a sense amplifier 220. Hereinafter, an operation of programming the resistive memory element M and an operation of reading data stored in the resistive memory element M are described.
During a program operation or rupture operation, a high voltage that may break a gate oxide of the c-fuse is applied to a gate G of the resistive memory element M. The high voltage is usually generated by a charge pumping method using a power source voltage greater than approximately 6V. Thus, the resistive memory element M operates as a resistor having a relatively low resistance value. When the resistive memory element M is not programmed, the resistive memory element M operates as a capacitor having a relatively high resistance value.
During a read operation, a voltage, which is appropriate for the read operation, for example, approximately 3V, is applied to the gate G of the resistive memory element M. Thus, a current path is formed through the data line DL and the load 210 from the resistive memory element M. Since the resistive memory element M has a relatively low resistance value when the resistive memory element M is programmed, a current flows through the load 210. The voltage level of the data line DL increases due to the flowing current. Since the resistive memory element M operates as a capacitor, that is, the resistive memory element M has a high resistance value when the resistive memory element M is not programmed a small current flows through the load 210. Thus, the voltage level of the data line DL is in a low state. The sense amplifier 220 generates output data DATA by comparing the voltage level of the data line DL with a reference voltage VREF.
Since enough current to sense the data flows through the data line DL, a relatively high voltage, for example, approximately 3V, has to be applied to the gate of the resistive memory element M during the read operation. Therefore, a power source voltage applied from an exterior, for example, less than approximately 1.5V, is used for the read operation by being boosted. However, the use of the high voltage brings a large burden to the read operation of the memory device. Although a voltage having a higher level, which ranges from approximately 6V to approximately 7V, has to be used during the program operation, the use of the high voltage does not bring a large burden to the program operation of the memory device since the program operation is not performed as frequently as the read operation.